Electromagnetic receiver and transmitter



Aug. 27, 1929. A. A. THMAs 1,726,200A

` ELECTROHAGNETIC RECEIVER AND TRANSMITTER Filed June 4, 1928 INVENTOR/WMV PatentedAug. 27, 1929. I

UNITED sT- A'TES ADoLrH A. THOMAS,

oFNEw Yonx, N.- Y.

` EILEcTnoMAeNETIc RECEIVER AND TRANSMITTER.

Application filed June 4,

I This invention is for an electromagnetic' translating device of novelconstruction and improved operation for converting electric impulses tomechanical vibration `and vice versa. One of the main uses of myinvention is for operating loudspeakers, especially those ofthe conetype. My new instrument is exceedingly simple and compact, and per mitsashort direct connection between armature and diaphragm without lostmotion, so that a high degree of efliciency is attained. My newelectromognetic device' in 4a preferred embodiment comprises a magnetframe having two pairs of pole pieces between which thepends of acentrally sup-o ported armature vibrate. The armature is rigidlyconnected at the center tothe central or neutral part of the fieldmagnet structure. The latter is preferably of circular or ell-ipticalshape with adiametric arm to which the armature is secured at rightangles thereto. The armature is an elastic reed free to vi-L, brate atboth kends andcarrying one orv two" polarizing coils. When operating l,alarge diaphragmfthe armature has both ends rigidly connectedfto thediaphragm by short stout rods which are free from disturbing vibrations.This short direct connection is possible because the driving unit as awhole can be mounted very close to the center of the diaphragm.

In the accompanying drawings, which illustrate two practicalembodiments-tof my Fig. 1 is a face'.-viewof an'electromagneticactuating unit for loudspeakers;

Fig.'2 is a section on line 2--2 of Fi`g. 1;'

Fig. 3 is a section on line 3-3 of Fig. 1;

Fig. 4 shows a perspective of the -ieldA magnet .frame u sed in theconstruction. of Figs. 1-3;

Fig. 5 shows amodification-employing two f U-shaped magnets; and

l Fig. 6 represents-a section on line 6.-6 of Fig. 5 to show how aportion ofthe field finzi is short-circuited for controlling theoperation of the instrument.

yReferring to Figs. 1-4, there 10 mounted in a casing orother suitablesupport 12. In the present instance,'the magnet 10 isa one-piecestructure substantially4 *circular .in shape, comprising adlametrlc arm'13 ,and two pairs of lateral extensions4 14' and 15. 'These/ extensionsterminate in isa magnet .secured at the center to the arm 13, as byrivets 22 or otherwise.- As seen 1n Fig. 1,-

1928. Serial N o. 282,589.

two pairs of pole pieces 16--16 and 17--17 which provide two airgaps 18and 18. For distinction I have marked the -pole pieces 16 and 16' assouth and north poles respectively,

^ neutral points by the cross-bar 13. The indicated polarity, however,is not essential, for the steel frame 10 canbe .so magnetized that thepole pieces 16 and 16 are of one polarity and the pole pieces 17--17 ofthe other polarity.` I n that case, the field iuX would pass4 throughthe diametric bar 13 and from there split into two'parallel pathsthrough the polar extensions v1414 and -15 across the two airgaps18--18. l

The magnet 10 may be solid or laminated, and can be punched A'from sheetsteel. It may be a permanent magnet, or of the elec# .tromagnetm type.The polar extensions 14 and 15 maybe made as separate pieces attached tothe arm 13, and those extensions need 'not be circular, but they maybeellipticalg rectangular, or of any other practical shape. A simple wayto secure ,the magnet titi 10' tothe support 12 is by providing thelatter with a pair of bosses 19 adapted to receive screws or bolts 20,which ,passthrolgh the ends of arm 13. It goes'without saying that thesupport 12 is of..nonmag`neti-c materiil and may b e cast-orf'molded asa single mei'nber' of aluminum, brass, bakelite., or any other materialu'seul for that purpose.

When the magnet 10 is cut or 4punched from sheet steel, thesemi-circular extensions 14 and .15 are .cutas a complete circle whichis slit at right angles to the arm 13. The v slit ends arethendlsplacedy relativel to each other, as indicated in Fig. 4. he polepieces 17 and 17 are 'attached separately to ,overlap the pole. pieces16 and 16.. There are other ,ways .of making the eld magnet, and thesuggestion just made is not to be considered-inet restrictive sense.

A flexible reedf or armature 21 rigidly the armature 21 is arrangedapproximately at right angles to the supporting arm 13, andGhefvibratory ends 23 and "24 of the armaturel extend into the magneticairgaps the coils 25 can be used like elastic pads con- 18 and 18respectively. When the armature 21 is at rest, its ends aresubstantially midway of the airgaps, as shown in Fig. 2. The vibratorymember 21 is prefeiably made of a magnetic metal or alloy having ahigher degree of permeability than the steel body of field magnet 10, sothat iiux variations produced in thearmature encounter the lowestpossible resistance. The strip or blade 21 canbe stamped out of solidsheetmetal,

or it may consist of thin magnetic laminae Welded together or otherwiserigidly secured.

The armature 21 is polarized by one or two coils 25 mounted on oppositesides of the central supporting arm 13. Only one coil is necessary, butI prefer to use two coils in series, so as to secure better magneticbalance and higher eiiiciency of the `instrument. The coils 25 are heldin place bya pair of non-magnetic brackets 26, which: are 4secured tothe arm 13 by suitable fastening stantly pressing against the armatureto dampen its movements without interfering with its instant response toiux variations produced by the speech coils. The inherent elasticity ofarmature 21 and the width of airgaps 18-j18 are so correlated thatl thearmature ends do not strike the pole pieces even when maximum currentpasses through coils 25. I y l The reed or armature 21 is connected to avibratory member 30, which is diagrammatically shown in Fig. 2 .as acone diaphragm. I want it understood, however,

` that in the broad aspect of my invention, the

part 30 represents any vibratory member capable, of performing a usefulinvention.

When the member 30 is a cone diaphragm,

theo latter -is preferably provided with al ring 31', which is connectedto the armature 21 by a pair of rods 32 of sufficient strength andrigidity. The ends of' these rods are firmly secured to armature 21 andyring 31 in any practical way, as by riveting, welding, screw-threadingand the like. rIhe rods 32 are preferably connected to ring 31 atdiametrically opposite points. Since the entire unit is lat and can bebrought close to diaphragm 30, the connecting rods 32 can be made veryshort, so as te be practically free from disturbing vibrations oftheinwown. This short direct connection between arma ture and diaphragmis of great. practical advantage, as will be understood by those favmiliarl with cone speakers.

The operation of the instrument will be clear from the precedingdescription, but I may summarize it in a few sentences. Referring toFig. 2, let us assume that at any instant the magnetic flux due to thespeech coil or coils 25 produces a south pole at 23 and a north pole at24. The armature ends will therefore be attracted toward the north pole17 and the south pole 17 respectively, A

and the diaphragm 30 is pulled toward the left (asviewed in Fig. 2).W'hen the speech flux in armature 21 produces a north pole at 23 and asouth pole at 24, the armature ends are attracted toward the-'southpole16 and the north pole 16 respectively, so that the diaphragm is nowpushed towardthe right,

These vibratory movements of the armature end's vary in direction andamplitude in accordance with the flux produced by the variable currentimpulses in'coils 25. I do not consider it necessary to show or describeany circuit connections for the coils, because the art is replete withtransmission and receiving systems in which the coils 25 can beconnected.

Attention is called to the fact that the vibratory movements of thearmature ends 23 and 24 are transmitted with increased lever- 'age tothe diaphragm 30, due to the fact that the rods 32 are connected to thearmature at acertain distance from the outer ends thereof. While such aconnection transmits the armature vibrations in decreased ratio to-thediaphragm, the resultant gain in poweris a highly desirable advantage,particularly in. I

large cone diaphragms that require less amof vibrationn and greaterdrivingl power. Also, it should be noticed that the plitude magneticeffect at the ends of the arma-ture is .two-fold the polarized ends arenot only attracted to the field poles of opposite polarity, but they arealso simultaneously re-y pelled by the otherfield poles. This cumu-4lative magnetic elfect at the armature ends cincreases the power andeiiciency of the instr ument. AThe diaphragm 30 is positively actuatedin both directions by a push-pull eifect. Another factor contributing tothe iid eiiicieiicy and sensitiveness of the instrument is thefact thatthe main field flux does not pass through the body of the armature. Thispermits the variable Hu'x -produced by the speech coils 25 to exert itsfull effect on the polaiends of the armature. The points at which therods 32 are connected to the arma-Y ture are so chosen in eachparticular design' of instrument as to obtain the best practicalresults. The nearer those connections are to the center of thearmature', the smaller will be the transmission ratio between armatureand diaphragm with correspondingly increased driving power. Conversely,by connecting the rods 32 to the armature at points ities 'indicated inFigs.'1, 2 and 3, the speech coils 25 are so Woundas to cause opposite-polarities at lthe ends of armature 21. As

previously mentioned, the magnet l() may be so polarized that the olepieces 16-1'6 are of one polarity and t e pole pieces 17--17 of theother polarity.` With a magnet so4 polarized, the coils should be soWound and .connected as to produce like polarities at the vibratory endsof the armature, in

order that the polarized armature ends shall,

vibrate simultaneously in the same direction 4to give the push-pulllefl'ect above described.

The magnetic arm 13, to which the armature 21 is connected in goodmagnetic contact,

provides a path for the talking flux when the coils produce like (andtherefore opposing) polarities at the center of the armature. p

In the modification of Figs. 5 and 6, the field magnet 33 consists'of apair` of U-shaped 'permanent magnets .34 connected along their. innerlegs 35. SinceA the outer legs 'are of opposite polarity, the inner legs35 consti- `tute-the neutral portion of the magnet. A

reed or armature 36 is rigidly connected at the center to the central-leg 35 ofthe magnet. A simple way of mounting the Aarmature on thefield magnet is by means of a- U-shaped magnetic'bracket 37 secured tothe neutral. leg 35 by a bolt or rivet 38, or otherwise. The armature 36is rigidly mounted on the magnetic bracket 37 by suitable fasteningmeans 39, which may be a rivet or the like. The coil or coils 25 are sowound and connected as to produce opposite polarities'l at the ends .ofarmature 36, which is connected to the .diaphragm 40 by Lrods 41? Thediaphragm 40 carries a ring 42 to which the rods 41 are connected, asmore fully explained in connection with Fig. 2. Asthe flux through thearmature 36. varies, the

free ends thereof are simultaneously attracted to and repelled by thefield poles 43 and 44. This will be understood without furtherexplanation.'

. The construction of 5 and 6inay be provided with means for regulatingthe effective field strengtht the pole pieces 43 and 44 byshort-circuitinv a portion vof the macgnetic flux. For this purpose`Imount a e'xible magnetic bladeor strip 45on a y ythe screw 49 is turneddown to force the yoke 47 against the flexible magnetic stripl 45, theends of the latter are brought closer to the outer limbs of the magnet,as roughly indicated by the dotted outline' 45. The

closer the ends of strip 45 are brought to the outer limbs of magnet 33,the greater will ged and easily assembled. My invent-ion` has specialadvantages as a driving unit for large diaphragms in loud speakers. Theshort-direct connection between armature and diaphragm eliminates lostmotion and undesirable vibrations. The double driving rods and theincreased power tranmission between armature and diaphragm make itpossiblefor a comparatively small instrument to operate efficiently alarge diahra m;

Although I have shown and described certain specific constructions, Iwant it distinctly understood that my invention is not limited to thedetails set forth. The basic features of my invention may bemechanically embodied in various other Ways Without departingfrom thescope of the invention as defined in the following claims.

I claim as my invention:

1. In an electromagnetic device, a flexible magnetic reed rigidlysupported at the eenter, means for polarizing said `reed, magnetic polesoperatively associatedy with the vibratory ends of said reed, andavibratory member connected to said reed.

2. In an electromagnetic device, a flexible Dmagnetic reed rigidlysupported at the center, means for polarizing said reed, magnetic polesoperatively associatedwiththe vibratory ends of said reed, a pair ofrods con-l nected to said reed near'its vibratory ends, anl a vibratorymember connected to said ro s.

3. In an electromagnetic device, the com- 'bination. of a field magnet,a flexible magnetic reed secured at the center to 'a neutral portion ofsaid magnet, the vibratory ends of said reed being in operative relationto the poles of said magnet, a vibratory member connected to said reednear the ends thereof, and 'a coil operatively associated with saidreed.

4. In an electromagnetic device, the combination of afield magnet havingtwo pairs of pole pieces arranged to provide two airgaps, a flexiblemagnetic reed secured at the center tothe central portion of saidmagnet, the vibratory. ends of v/said reed extending into said airgaps,a coilKl operatively associated with said reed, and a vibratory memberconnected to said armature.

5. As a new article of manufacture for use in electromagnetic devices, aeld magnet r consisting of a pair of lateral extensions connectedcentrally by a cross arm, said 'extensions terminating in overlappingpole pieces arranged .to provide two'airgaps.

6. As a -new article of manufacture for use inA electromagnetic devices,a field magnet I lconsisting of^apair of 'substantially semicircularextensions connected by a d1ametr1c arm, said extensions terminatng inpole -pieces arranged to provide two airgaps the ends of said reedextending into said a1rgaps, and a coil in operative relat1on to vsaidreed.

8. In an electromagnetic device, a flexible magnetic reed su ported forvibratory movement at one en magnetic pole pieces arranged in operativerelation to thevibratory end of said reed, a coil mounted on said reed`near its point of support, and means for holding said coil in place,said coil engaging said reed in yieldable pressure contact and therebyexerting a damping effect on its vibrations.

9.- In an electromagnetic device, a flexible magnetic reed rigidlysupported at the ce'nter, magnetic poles .operatively associated withthe vibratory ends of said reed, a pair of polarizing coils .mounted onsaid reed at opposite sides of its central support, said coils engagingsaid reed in yieldable pressure contact'to exert a damping effect on itsvibrations, and avibratory member connected to said reed. l

10. In an electromagnetic device, a flexible magnetic reed rigidlysupported at the' center, means for polarizing said reed, magnetic polesoperatively associated with the" vibratory ends of said reed, a pair ofrods connected to said reed at points between its central support andsaid magnetic poles, so that the vib ations at the free ends of saidreed are tr' nsmitted to said rods in decreased ratio and at increasedleverage, and a vibra- -torymember connected to said rods.

11. An electromagnetic translating device` comprising a field magnetstructure having 'a central portion and polar extensions. on oppositesides of said' central portion, an

. armature secured at the center to said lcentral portion of the magnetstructure, the free vibratory' ends of -said armature being in operativerelation to said polar'fextenslons,

means for polarizing said arfmature, and a.v

-vibratory member operatively connected to said armature.

12. An electromagnetic driving. unit for loudspeakers comprising a fieldmagnet structure having a central portion and polar extensions onopposite sides of said central portion, an armature secured at thecenter to said central portion of the magnet structure, the freevibratory ends of said armature being in operative relation to saidpolar extensions, a speech coil -surrounding said armature, a pair ofrods connected to said armature near the free ends thereof, and adiaphragm connected to said rods.`

13. An electromagnetm translating device comprising a field magnethaving a`pair-` of lateral extensions connected by a cross-arm, saidextensions terminatmg 1n pole p1eces arranged to provide two airgaps, anarmature secured at the center to the center of said arm, the `free endsof said armature extending into said airgaps for vibratory movement, acoil in operative relation to said armature, and a vibratory member-connected to said armature.

14. An electromagnetic translating device comprising a field magnethaving a pair of lateral extensions connected centrally by a cross-arm,said extensions terminating in` pole pieces arranged to provide twoairgaps, an armature secured at the center to the center'of said armsubstantially at right 4angles thereto, the free en ds of' said armatureextending intov said alrgaps for vibratory movement, a coil inoperativerelation to said armature, a paii` of rods connected to said armaturenear the free ends thereof, and a vibratory member connected 'to saidrods.

15.l An electromagnetic driving unit for loudspeakers comprising a fieldmagnet'having a pair of lateral extensions connected centrally by across-arm, said extensions terminating in pole pieces arranged toprovide two airgaps, an armature secured at the center to the center ofsaid arm' substantially at right angles thereto, the free ends of-saidarmature extending into said air- 'apsfor vibgatory movement, aspeech coil for said armature, a pair of rods connected to said armaturenear the free ends thereof,

and a diaphragm connected to s aid rods.

16. An electromagnetic driving unit for loudspeakers comprising a fieldmagnet having a pair of substantially semi-circular ex` tenslonsconnected by a dlametrlc arm, sald' extensions terminating in polepieces arranged to provide two airgaps, an armature securedatthe centerto the center of said diametric arm and substantially atright anglesthereto, the free ends of said'armature extending intosaid airgaps forvibratory movement, a coil in operative relation to said armatureya conediaphragm, and

connecting means between the end portions of said armature and saiddiaphragm.

17. An electromagnetic driving unit for loudspeakers comprising a fieldmagnet hav- 'ing a pair of substantially semi-circular extensionsconnected by a diametric arm, saidv extensions terminating in polepieces arranged to provide two airgaps, an armature secured at thecenter to the center of said diametric arm and substantially at rightangles thereto, the free ends of said armature extending into saidairgaps for vibratory movement, a pair of coils mounted on said armatureat opposite sides of its central support, means on said magnet to holdsaid coils 1n place, and a diaphragm connected to said armature near theends thereof.

18. An electromagnetic driving unit for loudspeakers4 comprising a fieldmagnet structure havinga central portion and polar extensions onopposite sides of said central portion, an armature secured at `thecenter to said central portion of the magnet structure, the vibratoryends of said armature being in operative relation to said polarextensions, a pair of speech coils mounted on said armature at oppositesidesfof its central support, a pair ofrods connected to said' armatureat points between said coils and said polar extensions, whereby thevibrations at the free ends of said' armature as transmitted to saidrods in decreased ratio and at' 19. An electromagnetic driving unit forV'l loudspeakers comprising a field Vmagnet structure having a centralvportion and. polar portion, an armature secured at the center tosaidcentral portion of the magnet structure, the 'vibratory ends ofSaidarmature l being in operative relation to said polar extensions, aspeech coil in operative relation to said armature, apair of rodsconnected to said armature near the free ends thereof, a cone diaphragmarranged substantially in axial alignment with the central portion ofsaid armature, a ring secured centrally to said diaphragm, and meansaforconnecting said rods to said ring.

20. An ,electromagnetic driving unit for loudspeakers comprising a fieldmagnet structure having a central portion and polar extensions onopposite sides of said. central portion,lan armature secured at thecenter to said central portion, of the magnety structure, the vibratory,ends of' said armaturebeing in operative relation tosaid polarextensions, a pair ofcoils mounted on said armature at opposite sides ofitscentral support, a pair of rods connected to said armature at pointsbetween said coils and said.

polar extensions, whereby the vibrations at 'the free ends of saidarmature are transmitted 'to said rods in decreased ratio and atincreased leverage, a cone diaphragm arranged substantially in axialalignment with the central portion of said armature, a ring securedcentrally to said diaphragm, and means for connecting said rods to saidring approximately at* diametrically opposite points.

' ADoLrH A. THOMAS.

